[2] Complexin is a small highly charged cytosolic protein that is hydrophilic, rich in glutamic acid and lysine residues.

Complexin acts as a positive regulator of synaptic vesicle exocytosis, and binds selectively to the neuronal SNARE complex.

[6] A possible mechanism for how complexin mechanistically anchors vesicles to prevent fusion involves inhibitory binding to the assembling SNARE complex.

[7] It is suggested that complexin's N-terminal alpha-helix domain incorporates itself into the SNARE complex helix bundle and prevents zippering of the assembly.

[4][8] In contrast to this, another hypothesis is that complexin, independent of synaptotagmin interactions, cross-links with SNARE complexes in a zig-zag array.

[9] In low levels of calcium, complexin has a comparatively stronger clamping and inhibitory effect on spontaneous vesicle release.